16 | Chapter 1
duties. There evidently has been time enough for the mate to cover im-
mense distances – but did he or she go north, south, east or west? Did
the outward and return journeys follow the same route, or was the over-
all track a loop? Can the absence be split into obvious and distinct trav-
elling and feeding phases? Only the recent arrival of tracking devices
has begun to provide answers to such questions.
Seabird biologists love to count seabirds, to the extent that we now
have a tolerably accurate estimate of the number of breeding pairs of
most species. Make some assumptions about how many immature birds
there are in the queue to join the colony, and it is possible to estimate
the number of each species on the wing. Add them together and there
may be some 700 million seabirds on earth, about one- tenth the number
of people. Especially numerous are the diving species of higher latitudes:
the penguins, shearwaters and auks. Knowing the food requirements of
birds of various sizes, it is possible to calculate the aggregate amount of
food they extract from the sea in a year. The total of at least 70 million
tonnes is remarkably similar to the amount, some 80 million tonnes, the
fishing industry has brought ashore each year since 2000.^11
This sketch of the sort of knowledge seabird biologists have accrued
from land- based studies might, one would think, be expanded by obser-
vations at sea. That is true to a degree. When North Sea oil production
was getting underway in the 1970s, numerous surveys were undertaken
to assess which parts of the basin were preferentially used by seabirds
that might fall foul of oil spills. Although such information may help
conservation planning, it reveals nothing about the origins of the birds
seen. In the same era, Pierre Jouventin and colleagues travelled south
from the French Département of La Réunion, in the tropical Indian
Ocean. Heading south towards Antarctica, they showed how certain
albatrosses, such as Wandering and Indian Yellow- nosed, and the Great-
winged Petrel, were seen most frequently near two zones where sea tem-
perature altered abruptly, the Sub tropical Convergence and the Antarc-
tic Polar Front.^12 This implies that the birds were seeking out these zones
of water- mixing and therefore enhanced marine productivity for feeding
(see Chapter 8). It tells us nothing about the colonies from which the
birds hailed, or whether they were breeders or non- breeders. Again it is